Fuel/air mixing system for fuel nozzle

ABSTRACT

A fuel nozzle includes an inner wall defining a central passage extending in an axial direction of the fuel nozzle, a hub wall surrounding the inner wall and defining a first annular passage, an outer wall surrounding the hub wall and defining a second annular passage, and a shroud surrounding the outer wall and defining a third annular passage. A swirler may receive air and direct the air into the first annular passage. The swirler includes at least one swirl vane extending from the shroud to the hub wall that has an air passage extending between the shroud and the hub wall. The air passage is coupled to the first annular passage and has a first width adjacent the shroud and a second width adjacent the hub wall. The second width is larger than the first width defining a diverging outlet into the first annular passage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/776,620, entitled “FUEL/AIR MIXING SYSTEM FOR FUEL NOZZLE,” filedFeb. 25, 2013, which is herein incorporated by reference in itsentirety.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to fuel nozzles, and morespecifically, to systems to increase fuel/air mixing within the fuelnozzles.

A gas turbine engine combusts a mixture of fuel and air to generate hotcombustion gases, which may be used to rotate a load, such as anelectrical generator. The gas turbine engine may include one or morefuel nozzles to direct the mixture of fuel and air into a combustionregion of the gas turbine. In addition, the one or more fuel nozzles maybe used to premix the fuel and the air. Unfortunately, poor mixing ofthe fuel and the air may reduce the flame stability within thecombustion region. In addition, non-uniform mixtures of fuel and air mayincrease the amount of undesirable combustion byproducts, such asnitrogen oxides.

BRIEF DESCRIPTION OF THE INVENTION

Certain embodiments commensurate in scope with the originally claimedinvention are summarized below. These embodiments are not intended tolimit the scope of the claimed invention, but rather these embodimentsare intended only to provide a brief summary of possible forms of theinvention. Indeed, the invention may encompass a variety of forms thatmay be similar to or different from the embodiments set forth below.

In a first embodiment, a system includes a fuel nozzle. The fuel nozzleincludes an inner wall defining a central passage extending in an axialdirection of the fuel nozzle, a hub wall surrounding the inner wall anddefining a first annular passage, an outer wall surrounding the hub walland defining a second annular passage, and a shroud surrounding theouter wall and defining a third annular passage. A swirler may receiveair and direct the air into the first annular passage, wherein theswirler includes at least one swirl vane extending from the shroud tothe hub wall. The at least one swirl vane has an air passage extendingbetween the shroud and the hub wall, and the air passage is coupled tothe first annular passage and has a first width adjacent the shroud anda second width adjacent the hub wall, and the second width is largerthan the first width defining a diverging outlet into the first annularpassage.

In a second embodiment, a system includes a vane curtain air swirlerthat may be disposed within a turbine fuel nozzle. The vane curtain airswirler includes one or more swirl vanes. Each swirl vane has a fuelplenum and a radial air passage that increases in width from an inlet toan outlet of the one or more swirl vanes.

In a third embodiment, a method includes directing a first portion ofair through a first annular passage between a shroud wall and an outerwall of a fuel nozzle. The method also includes directing a secondportion of air through a radial air passage of a swirler into a secondannular passage between a hub wall and an inner wall of the fuel nozzle.The hub wall surrounds the inner wall, the outer wall surrounds the hubwall, and the shroud wall surrounds the outer wall. The radial airpassage has a diverging outlet into the second annular passage.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic diagram of an embodiment of a gas turbine systemhaving a fuel nozzle with features to improve the mixing of fuel andair;

FIG. 2 is a perspective view of an embodiment of the fuel nozzles ofFIG. 1, illustrating the arrangement of the fuel nozzles within acombustor of the gas turbine system;

FIG. 3 is a cross-sectional view of an embodiment of one of the fuelnozzles of FIG. 2, illustrating a swirl vane with features to improvefuel/air mixing;

FIG. 4 is a cross-sectional view of an embodiment of the swirl vanes ofFIG. 3, taken along line 4-4, illustrating respective air passages withdiverging outlets to improve fuel/air mixing; and

FIG. 5 is a cross-sectional view of an embodiment of one of the swirlvanes of FIG. 4, taken within line 5-5, illustrating a diverging outlet.

DETAILED DESCRIPTION OF THE INVENTION

One or more specific embodiments of the present invention will bedescribed below. In an effort to provide a concise description of theseembodiments, all features of an actual implementation may not bedescribed in the specification. It should be appreciated that in thedevelopment of any such actual implementation, as in any engineering ordesign project, numerous implementation-specific decisions must be madeto achieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

When introducing elements of various embodiments of the presentinvention, the articles “a,” “an,” “the,” and “said” are intended tomean that there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.

The present disclosure is directed toward systems for improving fuel andair mixing within fuel nozzles. In particular, the fuel nozzle mayinclude a swirler to deliver air into an axial air passage defined by ahub wall of the fuel nozzle. The air flows downstream into one or morepremixing tubes (e.g., a group of 2 to 100 premixing tubes), where theair mixes with fuel and is subsequently directed into a combustionregion. The swirler imparts a swirl (e.g., circumferential velocity) tothe air. It is beneficial to control the amount of swirl to avoidnon-uniform mixing of the air and fuel within the premixing tubes. Poormixing of the air and fuel may reduce the flame stability in thecombustion region, may increase the formation of undesirable combustionbyproducts, such as nitrogen oxides, and may also increase thepossibility of combustion dynamics excitation. Decreasing the swirl ofthe air as it flows within the axial air passage may provide a generallyuniform distribution of the air into the premixing tubes. To this end,the swirler includes swirl vanes equipped with an inner wall defining aradial air passage. The radial air passage has a diverging outlet intothe axial air passage to ensure a generally uniform fuel/air profile ineach premixing tube. In particular, the width of the radial air passageincreases as it approaches the axial air passage. The diverging outletreduces the swirl of air into the premixing tubes, thereby increasingthe mixing of fuel and air, increasing flame stability within thecombustion region, and reducing the amount of undesirable combustionbyproducts.

Turning now to the figures, FIG. 1 illustrates a block diagram of anembodiment of a gas turbine system 10 with a fuel nozzle 12 (e.g.,turbine fuel nozzle) to increase mixing of fuel and air. Throughout thediscussion, a set of axes will be referenced. These axes are based on acylindrical coordinate system and point in an axial direction 14, aradial direction 16, and a circumferential direction 18. For example,the axial direction 14 extends along a length or longitudinal axis 17(shown in FIG. 3) of the fuel nozzle 12, the radial direction 16 extendsaway from the longitudinal axis 17 (shown in FIG. 3), and thecircumferential direction 18 extends around the longitudinal axis 17(shown in FIG. 3).

As illustrated, the gas turbine system 10 includes a compressor 20, acombustor 22 (e.g., turbine combustor), and a turbine 24. The turbinesystem 10 may include one or more of the fuel nozzles 12 described belowin one or more combustors 22. The compressor 20 receives air 26 from anintake 28 and compresses the air 26 for delivery to the combustor 22. Asshown, a portion of the air 26 is routed to the fuel nozzle 12, wherethe air 26 may premix with fuel 30 before entering the combustor 22. Theair 26 and the fuel 30 are fed to the combustor 22 in a specified ratiosuitable for combustion, emissions, fuel consumption, power output, andthe like. Unfortunately, if the air 26 and the fuel 30 are not wellmixed, the flame stability within the combustor 22 may be reduced.Accordingly, the fuel nozzle 12 includes a swirler with swirl vaneshaving diverging outlets to improve the mixing and uniformity of fueland air, as will be discussed further below.

After the mixture of the air 26 and the fuel 30 is combusted, the hotcombustion products enter the turbine 24. The hot combustion productsforce blades 32 of the turbine 24 to rotate, thereby driving a shaft 34of the gas turbine system 10 into rotation. The rotating shaft 34provides the energy for the compressor 20 to compress the air 26. Forexample, in certain embodiments, compressor blades are included ascomponents of the compressor 20. Blades within the compressor 20 may becoupled to the shaft 34, and will rotate as the shaft 34 is driven torotate by the turbine 24. In addition, the rotating shaft 34 may rotatea load 36, such as an electrical generator or any device capable ofutilizing the mechanical energy of the shaft 34. After the turbine 24extracts useful work from the combustion products, the combustionproducts are discharged to an exhaust 38.

As noted previously, the gas turbine system 10 includes one or more fuelnozzles 12 with features to improve the mixing and uniformity of the air26 and the fuel 30. FIG. 2 illustrates an arrangement of the fuelnozzles 12 within the combustor 22 of the gas turbine system 10. Asshown, six fuel nozzles 12 are mounted to a head end 40 of the combustor22. However, the number of fuel nozzles 12 may vary. For example, thegas turbine system 10 may include 1, 2, 3, 4, 5, 10, 50, 100, or morefuel nozzles 12. The six fuel nozzles 12 are disposed in a concentricarrangement. That is, five fuel nozzles 12 (e.g., outer fuel nozzles 42)are disposed about a central fuel nozzle 44. As will be appreciated, thearrangement of the fuel nozzles 12 on the head end 40 may vary. Forexample, the fuel nozzles 12 may be disposed in a circular arrangement,in a linear arrangement, or in any other suitable arrangement. The flowof the air 26 and the fuel 30 within the fuel nozzles 12 is discussedbelow with respect to FIGS. 3-4.

FIG. 3 is a cross-sectional view of an embodiment of the fuel nozzle 12equipped with a swirler 46 having swirl vanes 48 with diverging airoutlets 50 (more clearly shown in FIG. 4). The diverging outlets 50 maybe tapered, conical, and/or gradually increase in width to improvemixing of the air and the fuel in premixing tubes 70. In certainembodiments, it may be desirable to equip the outer fuel nozzles 42 withthe swirler 46 having the diverging air outlets 50 and to employ adifferent design for the central fuel nozzle 44. However, in certainembodiments, the central fuel nozzle 44 may be equipped with the swirler46 with the diverging air outlets 50. In other words, the swirler 46 maybe used within the outer fuel nozzles 42, the central fuel nozzle 44, orany combination thereof.

As illustrated, the fuel nozzle 12 includes an inner wall 51 defining acentral passage 54 (e.g., inner cylindrical passage). During operationof the fuel nozzle 12, liquid fuel or purge air for gaseous fuel usagemay be routed through the central passage 54 in the axial direction 14,as shown by arrows 56. A hub wall 58 defines a first annular passage 60.During operation of the fuel nozzle 12, the vane curtain air from theswirler 46 flows through the first annular passage 60 along arrows 62and into one or more premixing tubes 70. Again, the swirler 46 includesthe diverged air outlets 50 to reduce the swirl of the vane curtain air,thereby improving the operability of the fuel nozzle 12.

An outer wall 64 surrounds the hub wall 58, defining a second annularpassage 66. During operation of the fuel nozzle 12, the fuel 30 isrouted through the second annular passage 66 in the axial direction 14,as shown by arrows 68. The fuel 30 enters the premixing tubes 70 in theradial direction 16 through at least one fuel hole 71 (e.g., an openingor aperture) in the premixing tubes 70, as indicated by arrows 72.Within the premixing tubes 70, the fuel 30 mixes with the air 26 to forma combustible mixture and is directed into the combustor 22.

A shroud 78 (e.g., annular shroud wall) is disposed about the outer wall64, defining a third annular passage 80. A portion of the air 26 entersupstream of swirler 46 in axial direction 14 through the third passage80, mixes with the fuel injected from at least one fuel hole 79 coupledto fuel plenum 85 (e.g., fuel passage) within swirl vanes 48 and travelsin the axial direction 14 toward the outlet 74 of the fuel nozzle 12, asindicated by arrows 82. However, a second portion of the air 26 (e.g.,vane curtain air) enters the first annular passage 60 radially 16through the swirler 46, which includes the one or more swirl vanes 48circumferentially 18 spaced about an axis of the fuel nozzle 12. Thatis, the air 26 flows through one or more vane curtain air passages 49(e.g., radial air passages) within the swirl vanes 48. In certainembodiments, the vane curtain air may flow through one or more inletflow conditioners (e.g., a perforated annular sheet) to meter anddiffuse the air into the fuel nozzle 12. As noted above, the swirl vanes48 include the diverged air outlets 50, which reduce the circumferential18 swirl of the vane curtain air as it enters the first annular passage60. The diverging outlets 50 help to diffuse, reduce the velocity of,and generally straighten the flow of the vane curtain air toward thepremixing tubes 70 (e.g., toward inlets of the premixing tubes 70). Inother words, the swirl vanes 48 have two purposes: one to generate swirlin the passage 80, and another to deliver the vane curtain air withreduced or no swirl into the first annular passage 60. The reduced swirlof the vane curtain air increases the flame stability within thecombustor 22 and reduces the formation of undesirable combustionbyproducts.

As shown, the premixing tubes each have an axial air inlet 73 at one end75 of the tube 70, one or more lateral fuel inlets 71 in a side wall 77of the tube, and an axial outlet 83 at an opposite end 87 of the tube 70that discharges a fuel/air mixture from each premixing tube 70. Asillustrated, diverging outlet 50 of the swirl vanes 48 substantiallyreduces the swirl (e.g., circumferential velocity) of the vane curtainair along the first annular passage 60 as it travels in the axialdirection 14. Indeed, when the vane curtain air enters the premixingtubes 70, the circumferential velocity is substantially less than theaxial velocity of the vane curtain air. In certain embodiments, theswirl velocity may be approximately zero. The reduced swirl velocity mayresult in a more uniform distribution of air in each premixing tube 70and among the premixing tubes 70, thereby improving the efficiency andoperability of the fuel nozzles 12.

Within the premixing tubes 70, the straightened vane curtain air mixeswith the fuel 30, which flows radially into the premixing tubes. As willbe appreciated, the reduced swirl velocity of the vane curtain air mayalso result in a more uniform equivalence ratio (i.e., ratio of theactual fuel/air ratio to the stoichiometric fuel/air ratio) in eachpremixing tube 70 and between the premixing tubes 70. For example, theequivalence ratios within each premixing tube 70 may be betweenapproximately 0.3 to 0.7, 0.4 to 0.6, or 0.53 to 0.56, and all subrangestherebetween. The increased uniformity of equivalence ratios among thepremixing tubes 70 improves the mixing of the fuel 30 and the air 26,thereby improving the flame stability within the combustor 22 andreducing the amount of undesirable combustion byproducts. As notedabove, the combustion of the fuel 30 and the air 26 is made moreefficient by the diverging outlet 50 within of the swirl vanes 48, thegeometry of which will be described in greater detail below.

FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. 3illustrating an embodiment of the swirler 46 having the divergingoutlets 50 within each swirl vane 48. As shown, the swirl vanes 48extend from the shroud 78 to the first annular passage 60. In addition,the swirl vanes 48 include air passages 49 (e.g., vane curtain airpassages 49) that extend radially 16 along a length of the swirl vane 48from the shroud 78 to the hub wall 58. The air passages 49 include thediverged outlets 50 to diffuse the air flow, reduce the circumferentialvelocity of the air flow, and generally straighten the air flow of thevane curtain air entering the first annular passage 60. The fuel 30flows through the second annular passage 66 (shown in FIG. 3) into oneor more fuel holes 79 coupled to fuel plenum 85 (shown in FIG. 3) andthrough the cylindrical fuel passage 81 into the fuel holes 71 on theside wall of the premixing tubes 70. Within the premixing tubes 70, theuniformity of the fuel 30 and the air 26 is improved, such that theequivalence ratio within each premixing tube 70 is approximately equal,as discussed previously.

FIG. 5 illustrates an embodiment of one of the swirl vanes 48 having thediverging outlet 50 taken within the line 5-5 of FIG. 4. As shown, theswirl vane 48 has an inlet 61 (e.g., the vane curtain air inlet 68) andan outlet 63 into the first annular passage 60. The swirl vane 48 has aninlet width 84 adjacent the shroud 78 and an outlet width 86 adjacentthe hub wall 58. Notably, the outlet width 86 is larger than the inletwidth 84, defining the diverging outlet 50. The transition from theinlet width 84 to the outlet width 86 reduces the swirl of (e.g.,straightens) the air 26 within the first annular passage 60 and diffusesthe air flow, thereby improving the uniformity of the air 26 and thefuel 30 within the combustor 22.

As illustrated, the vane curtain air passage 49 within the swirl vane 48has a constant width portion 88 and a varying width portion 90, and atransition point 92 disposed therebetween. The constant width portion 88extends along a length 94 of the swirl vane 48 radially 16 from theinlet 61 to the transition point 92. Within the constant width portion88, the width of the swirl vane 48 (i.e. inlet width 84) isapproximately constant. In addition, the varying width portion 90extends along a length 95 of the air passage of the swirl vane 48. Thewidth (e.g., 84 and 86) of the vane curtain air passage 49 within theswirl vane 48 gradually changes (e.g., diverges or enlarges along theaxial 14, radial 16, and/or circumferential 18 directions) from thetransition point 92 to the outlet 63 along the length 96 of the varyingwidth portion 90. In certain embodiments, the width (e.g., 84 and 86) ofthe air passage of the swirl vane 48 may vary along an entire length 95of the swirl vane 48. That is, the swirl vane 48 may not include theconstant width portion 88 and the transition point 92.

The swirl vane 48 also includes a centerline 98 extending radially 16from the shroud 78 to the hub wall 58. The centerline 98 is offsetrelative to the longitudinal axis 17 (shown in FIG. 3) of the fuelnozzle 12. The centerline 98 divides the swirl vane 48 into two sections100 and 102. As will be appreciated, the shape of the swirl vane 48 mayvary. Thus, in certain configurations, the centerline 98 may define anaxis 112 of symmetry of the swirl vane 48, and the sections 100 and 102may be identical. As shown, the sections 100 and 102 form correspondingangles 104 and 106 with the reference lines 108 and 110. The angles 104and 106 are formed relative to the internal surface 114 of the divergingoutlets 50. The references lines 108 and 110 are parallel to thecenterline 98 and are crosswise to the longitudinal axis 17 (shown inFIG. 3) of the fuel nozzle 12. In other words, the angles 104 and 106are formed relative to the centerline 98. The angles 104 and 106 aregenerally different and are designed to impart a minimum circumferentialvelocity to the air 26 as the air passages through the diverging outlets50 into the first annular passage 60. The angles 104 and 106 may varyaccording to the shape of the swirl vane 48 and/or the diverging outlet50, and thus may be implementation-specific. For example, each of theangles 104 and 106 may be between approximately 1 to 50, 5 to 25, or 10to 15 degrees, and all subranges therebetween. Further, the angles 104and 106 may be different from each other.

Technical effects of the disclosed embodiments include systems andmethods for improving the mixing of the air 26 and the fuel 30 withinthe fuel nozzles 12 of a gas turbine system. In particular, the fuelnozzle 12 is equipped with the swirler 46 having the diverging outlets50 in the swirl vanes 48. In other words, the width of the air passages49 increases toward the hub wall 58. The diverging outlets 50 reduce thecircumferential velocity of the air 26, thereby increasing theuniformity of the air 26 and the fuel 30 within the fuel nozzle 12. Theincreased mixing of the air 26 and the fuel 30 increases the flamestability within the combustor 22 and reduces the amount of undesirablecombustion byproducts.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

The invention claimed is:
 1. A system, comprising: a vane curtain airswirler configured to be disposed within a turbine fuel nozzle,comprising: one or more swirl vanes, each swirl vane comprising: a fuelplenum; and a radial air passage that increases in width from an inletto an outlet of the radial air passage.
 2. The system of claim 1,wherein the radial air passage comprises a first portion and a secondportion, wherein the width of the radial air passage along the firstportion is constant, and wherein the width of the radial air passagealong the second portion gradually increases.
 3. The system of claim 2,wherein the radial air passage comprises a centerline extending from theinlet to the outlet, the centerline divides the radial air passage intofirst and second sections, the first section of the second portion formsa first angle relative to the centerline, the second section of thesecond portion forms a second angle relative to the centerline, and thefirst angle is different than the second angle.
 4. The system of claim2, wherein the second portion of the radial air passage at its widestwidth is configured to couple to an annular passage disposed within theturbine fuel nozzle, wherein the annular passage is defined by an innerwall that defines a central passage extending in an axial direction ofthe turbine fuel nozzle and a hub wall surrounding the inner wall. 5.The system of claim 2, comprising the turbine fuel nozzle wherein theone or more swirl vanes comprises a plurality of the swirl vanes, andthe plurality of swirl vanes is disposed circumferentially about theturbine fuel nozzle.
 6. The system of claim 5, comprising a gas turbineengine, wherein the gas turbine engine comprises the turbine fuelnozzle, a turbine combustor having the turbine fuel nozzle, acompressor, and a turbine.
 7. A turbine fuel nozzle, comprising: aninner wall defining a central passage extending in an axial direction ofthe turbine fuel nozzle; a hub wall surrounding the inner wall anddefining a first annular passage; an outer wall surrounding the hub walland defining a second annular passage; a shroud surrounding the outerwall and defining a third annular passage; and a vane curtain airswirler comprising one or more swirl vanes, wherein each swirl vanecomprises: a fuel plenum; and a radial air passage that increases inwidth from an inlet adjacent the shroud to an outlet adjacent the hubwall.
 8. The turbine fuel nozzle of claim 7, wherein the radial airpassage comprises a first portion and a second portion, wherein thewidth of the radial air passage along the first portion is constant, andwherein the width of the radial air passage along the second portiongradually increases.
 9. The turbine fuel nozzle of claim 8, wherein theradial air passage comprises a centerline extending from the inlet tothe outlet, the centerline divides the radial air passage into first andsecond sections, the first section of the second portion forms a firstangle relative to the centerline, the second section of the secondportion forms a second angle relative to the centerline, and the firstangle is different than the second angle.
 10. The turbine fuel nozzle ofclaim 8, wherein the second portion of the radial air portion at itswidest width is configured to couple to the first annular passagedisposed within the turbine fuel nozzle.
 11. The turbine fuel nozzle ofclaim 8, wherein the vane curtain air swirler comprises a plurality ofthe swirl vanes disposed circumferentially about the turbine fuelnozzle.
 12. The turbine fuel nozzle of claim 8, wherein the firstportion is disposed between the shroud and a transition point betweenthe hub wall and the outer wall, and the second portion is disposedbetween the transition point and the hub wall.
 13. The turbine fuelnozzle of claim 7, wherein the vane curtain air swirler is configured toreceive air in a radial direction crosswise to the first annularpassage.
 14. The turbine fuel nozzle of claim 7, wherein each swirl vaneof the one or more swirl vanes comprises one or more fuel holes coupledto the fuel plenum and configured to route fuel into the third annularpassage.
 15. The turbine fuel nozzle of claim 14, wherein the radial airpassage of each swirl vane of the one or more swirl vanes is configuredto route air through the respective swirl vane axially into the thirdannular passage to mix with the fuel routed through the one or more fuelholes.
 16. The turbine fuel nozzle of claim 7, comprising a plurality ofpremixing tubes extending in the axial direction and coupled to thefirst annular passage, wherein the plurality of premixing tubes have oneor more fuel holes configured to receive fuel from the second annularpassage, wherein the plurality of premixing tubes is configured toreceive a generally uniform distribution of air, to mix the fuel and theair, and to direct a mixture of the fuel and the air to an outlet of theturbine fuel nozzle.
 17. A system, comprising: a vane curtain airswirler configured to be disposed within a turbine fuel nozzle and toreceive air and to direct the air into an annular passage disposedwithin the turbine fuel nozzle, wherein the annular passage is definedby an inner wall that defines a central passage extending in an axialdirection of the turbine fuel nozzle and a hub wall surrounding theinner wall, and the vane curtain air swirler comprises: at least oneswirl vane configured to extend from a shroud surrounding both the innerwall and the hub wall, the at least one swirl vane comprising an airpassage, wherein the air passage is coupled to the annular passage has afirst width adjacent the shroud and a second width adjacent the hubwall, and the second width is larger than the first width defining adiverging outlet into the annular passage.
 18. The system of claim 17,comprising the turbine fuel nozzle having the vane curtain air swirler.19. The system of claim 17, wherein the air passage comprises a firstportion configured to be disposed between the shroud and a transitionpoint between the hub wall and an outer wall surrounding the hub wall,and the air passage comprises a second portion between the transitionpoint and the hub wall, and wherein a width of the air passage graduallyexpands along the second portion of the at least one swirl vane in aradial direction toward the hub wall.
 20. The system of claim 19,wherein the width of the air passage is constant along the first portionof the at least one swirl vane.